Thursday, November 29, 2012

Some Gas in Every Tank and a Lie in every Fuel Gauge [tf charts]

Sort of off topic, but practical, so here you go.

So this morning i get into the car a little late, and notice that my gas fuel gauge has the needle steady riiiight about the 1/4 tank mark.  One way for me is 26 miles, so my brain said "yeah, I should be good."  I mean looking at it physically, 1/4 of a 16 gallon should net me about 115 miles.  But it's not true.  IT'S ALL LLLIIIEEESSSS.  Click the image to see it full sized and legible.

In my gut I knew better.  All the cars I've driven suffer from a similar issue - the gauge drops from full to 3/4 at a very slow rate.  then from 3/4 to 1/4 it plummets like a stone, only to slow down again at the 1/4 mark.  Of course my gut was right.  Over 26 miles 1/4 dropped to 0 and that fun little fuel light went on, luckily enough to get from work to the gas station.

You see this auto builders?  That noise just ain't right.


  1. SO SO SO TRUE. Ugh. Stupid cars.

  2. Yeah, this always bothered me, but there is a reason.

    Gas tanks are shaped to the car, meaning that most gas tanks are not exact rectangles, but rather look like this (not to scale)

    | |
    | /
    | /
    | /

    This is one of the reasons that the the gauge is really difficult for auto manufactures to get right. Also, the position of the car to the ground play into this as well. Due to the shape, if you park on a upward hill, the gas tank will read more than is in there, downward hill, generally less than what is in there.

    Since gas tanks are not a closed system within a car, it is really difficult to get an accurate and consistent measurement, it would be great, but I don't think anyone has done this a good way at this point.

  3. argh, bad commenting system. That highly skilled drawing should have looked like a rectangle with the bottom right corner cut out.

  4. haha i get the jist from that awesome ascii art brick.